Ventilated benches

A ventilated bench is a bench which has some sort of fume removal system driven by a fan which can be switched on or off. They are especially useful for chemicals with low volatility. Ventilated benches have been shown to be as successful as fume hoods in dealing with hazardous fumes.

They also have the benefit of allowing simple access and therefore are likely to cut down on certain types of accidents such as those involving blades and other sharp implements. They are particularly useful for autopsies or dissection. The disadvantages of a ventilated benches is that is that they may not protect against particles as a result of an explosion or localised heating.

Note that Ventilated benches do not protect the user from infectious risk of microbes – they are only useful for limiting potential exposure to fumes. Where the ventilated bench is use for work with micro-organisms, then the final extract must pass through a HEPA (High efficiency particulate absorption) filter.

Construction

Ventilated benches are often made of stainless steel and have a perforated work surface. Ventilated benches are usually supported on a sold frame structure. Many have with removable panels in the front to enable easy access.

Transport of air in ventilated benches is either:

1. Downwards through the perforated work surface via a central spigot
2. Horizontally across the worktop via air grilles located in the rear of the bench.

If you need more accurate control of the flow of air on a ventilated bench, a variable speed fan can be fitted. The fan will let the operator accurately set the correct airflow for a particular experiment.

Horizontal ventilation

Positioned on the back wall of the bench and extracts air across the bench. It’s efficiently is limited by he fact that the draw is higher at the back of the bench than at the front which is the furthest point from the duct. Since the operator works at the front of the bench, protection is limited.

Down Draft Ventilation

Ventilated benches with down draft ventilation are very efficient at removing fumes. They have a perforated work surface and fumes are drawn away evenly across the worktop. This type of bench allows easy access to work and are good alternatives to fume cupboards as they are not restricted by walls and give freedom of hand and arm movement and better vision.

Buying advice

If buying a ventilated bench with a perforated work surface, make sure that the work surface can be removed for cleaning and decontamination. Look out for ergonomic designs which offer the operator full length knee space when using the bench in a sitting position, and standard bench height for use when standing up.

Advice on using ventilated benches

1. Do not cover more than one third of the bench, otherwise there will not be enough suction to remove fumes
2. Do not use for techniques more than 40 to 50 degress C.
3. Work close to the perforated bottom or side fan
4. Ensure the ventilated bench is designed and fitted to recognised standards (always ask for proof from the supplier)

Selective suction nozzles

These are devices that can be used when working with noxious chemicals and equipment that are too big to use on a ventilated bench or fume cupboard/hood.

Fume cupboards

FUME CUPBOARDS